Rocket science has evolved tremendously over the years, with a variety of propellants being used to reach the stars. One such fuel that has grown in popularity is liquid methane. The driving force behind this interest is its clean-burning properties, its ability to be produced off-world, and its high performance. How is liquid methane produced for rocket fuel?
Extraction and Purification
Liquid methane production begins with the extraction of natural gas. Natural gas is a hydrocarbon gas mixture primarily composed of methane, and is typically found in underground reservoirs, often in association with petroleum. The extraction of this gas relies on advanced drilling techniques, and once the natural gas is extracted, it is a blend of several gases and impurities.
To isolate methane, the raw natural gas undergoes a series of processing and purification steps. These steps remove other hydrocarbon gases (such as ethane, propane, butane), as well as inert gases, sulphur compounds, and water vapor. The end result is nearly pure methane, which is then ready for the next stage in the process.
Liquefaction
Once the purified methane gas is ready, it is converted into liquid form through a process known as liquefaction. This involves cooling the gas to a temperature below its boiling point, -161°C or -258°F at atmospheric pressure. In this cooled, condensed state, methane is much more compact, occupying about 1/600th of its original volume, which makes it easier to store and transport.
For use in rocket engines, this liquid methane, now in a denser and more energy-rich state, is highly suitable as a propellant. However, it may need further treatment to ensure its purity and quality are to the required standards.
Liquid Methane in Rocketry
Space companies, such as SpaceX, are investing heavily in methane-based propulsion. The company’s Raptor engine, designed for their Starship vehicle, uses a combination of liquid methane and liquid oxygen as fuel. This combination is known as a methalox propellant.
The interest in liquid methane extends beyond its clean-burning properties and performance. SpaceX’s CEO Elon Musk has talked about producing liquid methane directly on Mars using local resources, specifically carbon dioxide from the Martian atmosphere and water from its icy soil. This process, known as in-situ resource utilization (ISRU), could be a game-changer for space exploration.
This potential production of methane from carbon dioxide and water, using a process called the Sabatier reaction, would involve splitting water into hydrogen and oxygen through electrolysis, and then combining the resulting hydrogen with carbon dioxide to produce methane and water. The energy required for this process could potentially be supplied by nuclear power or solar panels.
Future Implications and Sustainability
While methane is a potent greenhouse gas, it burns cleaner than other hydrocarbon fuels, producing less carbon dioxide per unit of heat released. This gives it an advantage in terms of emissions and environmental impact. If the production process can be powered by renewable energy sources or if methane can be harvested directly from biogas or produced off-world, this would add a dimension of sustainability to this promising rocket fuel.
It’s important to note that this field is rapidly evolving, with new technologies and processes under development. As we continue to push the boundaries of space exploration, the production and use of liquid methane as rocket fuel will likely continue to be an important area of research and development.
